The present invention relates to coatings used in joints of an exhaust system of internal combustion engines, and more particularly to a seal between an exhaust manifold outlet and an exhaust pipe inlet.
Contact surfaces of parts needing a sealed joint traditionally rely on gaskets because direct contact of the surfaces does not adequately seal the joint without expensive, fine machining of the surfaces. Gaskets, which generally comprise one or more layers of a malleable material, are employed to prevent the escape or leakage of gas between two contact surfaces that are bolted together. This task can be difficult to accomplish in high-temperature, high-pressure environments, such as that of an internal combustion engine. Known applications include the placement of a gasket, usually metallic, between the exhaust manifold and an exhaust pipe. The gasket is intended to provide an exhaust seal at the interface between the manifold and pipe that prevents combustion byproducts from escaping into the engine compartment of a vehicle.
Gaskets, however, have several drawbacks. Because of the high temperature, high pressure environment of the manifold/pipe interface, gaskets used in such environments are often made of specialized and expensive materials. Furthermore, the proper assembly of the manifold/pipe interface with a gasket can be labor intensive and time consuming, because even a small deviation from optimal placement can lead to a leaky seal. The operational environments of gaskets contribute to the inability of gasket to maintain a proper seal. Engine vibration tends to cause the gaskets to move, while high temperatures tend to degrade the gasket. Furthermore, even with gaskets, the contact surfaces of the manifold and pipe need to be finely machined.
Maintaining the seal at the manifold/pipe interface is important because leakage allows combustion byproducts into the engine compartment of a vehicle. This misdirection of exhaust gases prevents their proper conditioning before exhausting to the atmosphere. In addition, the leakage also increases engine noise, just as any hole in the exhaust system upstream of the muffler would also increase engine noise.
Thus, there exists a need for an efficient, recyclable, and economical improved seal between the exhaust manifold and the exhaust pipe.
The present invention provides a seal for use in a vehicle engine, which includes a first component that resists decomposition at the operating temperature of the vehicle engine and has a low coefficient of friction, and a second component that augments the sealing properties of the first component.
Another aspect of the present invention provides an exhaust system of a vehicle engine, which includes an exhaust manifold having a sealing surface, an exhaust pipe also having a sealing surface and a coating disposed between the sealing surfaces of the exhaust manifold and the exhaust pipe. The coating includes a first component that resists decomposition at the operating temperature of the vehicle engine and has a low coefficient of friction, and a second component that augments sealing properties of the first component.
A third aspect of the present invention provides a method of sealing an interface between an exhaust manifold and an exhaust pipe. The method includes providing an exhaust manifold with an outer sealing surface and an exhaust pipe with an inner sealing surface, applying a coating to the outer sealing surface or to the inner sealing surface or to both surfaces, and contacting the inner and outer sealing surfaces. The coating includes a first component that resists decomposition at the operating temperature of the vehicle engine and has a low coefficient of friction, and a second component that augments the sealing properties of the first component.
Seal coatings offer certain advantages over conventional sealing techniques. The seal coating obviates the need for gaskets, and minimizes problems associated with their use. Furthermore, the coating will level unevenness in the surface to be sealed, thus allowing the use of surfaces that are not finely machined, while still maintaining a tight sealing connection. Also, the coating has slip characteristics that allow sealed components to move without eroding the coating. The coating of the present invention is particularly useful in high temperature environments such as the exhaust systems of motor vehicles.